Gate driver circuits used to drive the gates of high-side and low-side N-channel MOSFETS (“N-MOSFETS”) typically include a bootstrap circuit to provide a floating power supply for the gate of the high-side N-MOSFET. The floating power supply provides a voltage level sufficient to bias the gate of the high-side N-MOSFET relative to the source thereby causing the high-side N-MOSFET to turn on (i.e., conduct current). In some applications, turning on the high-side N-MOSFET causes a power supply to be coupled to a load.
Bootstrap circuits are often implemented using a capacitor that is charged via current supplied through a bootstrap diode in series with a bootstrap resistor connecting to a low-side voltage supply. When the capacitor is sufficiently charged, the high-side N-MOSFET is turned on causing the bootstrap diode to be subjected to a reverse bias voltage commensurate with the magnitude of the voltage rating of the power supply. To ensure proper operation, the bootstrap diode technology is chosen to block the reverse bias voltage. By way of example, a bootstrap diode device used in an application having a 100 volt (V) power supply must be able to block a reverse bias voltage of 100V.
Unfortunately, many applications require a 200V power supply or have to withstand 200V of supply surges. However, the development of new technology to support a single-chip gate driver integrated circuit having a bootstrap diode rated to withstand 200V can be both costly and time consuming. Although single-chip gate driver circuits having a bootstrap diode rated for 100V are commercially available, a bootstrap diode rated to withstand a maximum reverse bias voltage of 100V will get damaged when exposed to a reverse bias voltage of 200V and, thus, cannot be reliably used to operate with a 200V power supply. As a result, bootstrapping a gate driver circuit on an integrated circuit (IC) that may be subject to a high reverse bias voltage (e.g., >200V) typically requires extra pins on the IC and components (e.g., a 200V diode) external to the IC, which raises system complexity and cost.